fasterize: Fast Polygon to Raster Conversion

Provides a drop-in replacement for rasterize() from the 'raster'
package that takes 'sf'-type objects, and is much faster. There is support
for the main options provided by the rasterize() function, including
setting the field used and background value, and options for
aggregating multi-layer rasters. Uses the scan line algorithm attributed to
Wylie et al. (1967) <doi:10.1145/1465611.1465619>.